Extracting sucrose from sugar cane



Get. 22, 1963 s. l. ALDRICH ETAL" 0 EXTRACTING SUCROYSE FROM SUGAR CANE F'iledsept. 12, may

' 3- Sheeps-Shget 1 22, 1963 B. l. ALDRICH ETAL I 3,107,605

EXTRACTING SUCROSE FROM SUGAR CANE Filed Sept. 12, 1961 3 Sheets-Sheet 2 Oct. 22, 1963 B. 1. ALDRICH ETAL 3,107,605 EXTRACTING SUCROSE FROM SUGAR CANE Filed Sept. 12, 1961 5 Sheets-Sheet 3 United States Patent EXTRACTING UCROSE FRGM SUGAR CANE Barry I. Aldrich, East Roseviile, New South Wales,

Ronald Frew, West Pennant Hills, New South Wales,

John R. Miller, Waliroonga, New South Wales, and

Peter C. Rayner, Manly, New South Wales, Australia,

assign'ors to The Colonial Sugar Refining Company Limited, Sidney, New South Wales, Australia, a company of Australia Filed Sept. 12 1961, Ser. No. 137,638 Claims priority, application Australia Sept. 23, 1960 3 (Ilaims. (Cl. 100-75) The invention relates to a method and apparatus for extracting sucrose from sugar cane, and more particularly to improvements to increase the yield from such sugar cane and to decrease the cost of extraction.

In one of the known methods, sugar cane stalk-s are first reduced to particle size so that they can be fed into a roller mill or crusher. The cane particles are subjected in this mill to very heavy pressure so that the individual juice bearing cells of the cane are deformed and fractured to a large extent. In this way, a major portion of the juice is pressed out of the cane and can be drained away.

Cane residue, hereinafter referred to as bagasse, is passed out of the mill in the form of a kind of pulp comprising fibrous components of the cane and residual sugar juice not extracted in the first This bagasse is then treated with a washing or maceration liquid, by either spraying the liquid onto the bagasse or by immersing the bagasse in the liquid.

The maceration liquid is designed to dilute the residual sugar juice contained in the interstices between the bagasse fibres and on the external surfaces of the fibres and on the internal surfaces of the walls of the broken cells so that when the bagasse is passed through a further crushing mill or mills the residual juice will be extracted.

The above outlined method can be repeated several times to extract as much juice as possible.

These known methods have, however, the disadvantage that the effectiveness of the maceration or washing operation is impaired because the washing liquid is unable to enter completely into the broken cells and/ or interstices between the fibres and so dilute the residual juice therein. This incomplete entry of the liquid into the broken cells is thought to be caused mainly by the presence of air bubbles within the bagasse. These air bubbles enter the bagasse at the point where the latter leaves the last roller of the first crushing mill and expands owing to the re-' sure while the maceration liquid is applied to it.

No apparent advantage, however, has been gained from this method, because as soon as the roller pressure on the bagasse is relieved, air is drawn into the broken cells with the maceration liquid, and thus air pockets occur again.

It is an object of the invention to overcome the aforementioned problems, and thus to increase the efiiciency of the extraction method.

According to the invention, the bagasse is passed in a compressed state from the mill outlet directly into the maceration liquid for expansion therein, said liquid forming a seal for the outlet and preventing any air from being drawn into the bagasse. Thus during expansion, no air whatsover can be drawn into the various broken cells or interstices within the bagasse; every part of the bagasse except the internal surfaces of unbroken cells is wetted by the maceration liquid, and the so treated bagasse is then passed to the next mill. The efliciency of extraction is increased due to the more complete dilution of the lCC residual juice by the maceration liquid which reaches every broken cell and interstice in the bagasse.

Several ways of discharging the bagasse from the mill under liquid seal can be devised. In one form, the discharge opening of the crush-ing mill extends into a tank filled with maceration liquid, so that the bagasse after leaving the mill, expands within that liquid, and is then transported out of this tank to the next milling stage.

In another case, a similar liquid seal is provided at the mill outlet, but of such a shape that the mixture of bagasse and surplus maceration liquid overflows from the sealing trough into a further receptacle from which it is transported to the next mill.

The above arrangements can be further improved by a liquid seal arrangement in which the bulk of the surplus liquid is drained from the bagasse before the latter leaves the sealing arrangement. Thus the bagasse is suitable for handling on belt conveyors or the like and with minimum further drainage is suitable for feeding into a subsequent mill.

It has been found that with the invention outlined above, an improvement in extraction is obtained at each of the successive mills of a tandem giving an overall improvement approaching 1.0% in the sugar extracted, provided that all mills in the tandem, except the last one, are equipped with the invention. Further advantages resulting from the invention will appear hereinafter.

The invention will be described hereinafter in more detail in connection with the drawings in which:

FIGURE 1 shows schematically a sugar mill stage incorporating one embodiment of the invention;

FIGURE 2 shows schematically the sugar mill stage of FIGURE 1 incorporating another embodiment of the invention;

FIGURE 3 is a side elevation of the embodiment of FIGURE 2 with modifications showing details of the new liquid seal at the output of a sugar mill stage;

FIGURES 4 and 5 show details of the embodiment of FIGURE 3;

FIGURE 6 is a perspective view of part of the embodiment shown in FIGURE 3.

Referring to FIGURE 1 three rollers l, 2 and 3 rotating in the direction as indicated by the arrows form a sugar mill stage. These rollers are rotatably mounted between side cheeks and driven by suitable driving means of conventional design.

The sugar cane 4 previously broken up into particle size is fed into the mill by a suitable chute 5. At the output side of the mill a trough 6 is arranged in such a manner that the discharge or output opening of the mill is completely enclosed by the trough 6.

The level of liquid in trough 6 is maintained above the output opening of the mill stage by maceration liquid 7 supplied through an inlet 8. Visual evidence that the outlet of the mill is properly sealed is obtained by allowing the liquid to also fill the space between the trough front plate and roller 2 as indicated by the dotted level line 39.

The bagasse resulting from the crushing of the sugar cane particles 4 is thus discharged from the rollers 2 and 3 in a compressed state under the liquid seal in trough 6, where the bagasse expands under complete exclusion of air. Suitable conveying means 9 extend into trough 6 to transport the bagasse 7 to another mill stage or other location.

In the arrangement shown schematically in FIGURE 2 the trough 13 is funnel-shaped and is arranged at an angle so that the outer edge of the lower plate of the funnel forms an overflow edge 14 which is connected over a slide 15 with a further receptacle 17 into which the conveyor means 9 extend.

Two inlets 8 and 16 are provided in the top and bottom plates of the funnel-shaped trough 13 to pass the maceration liquid into the funnel and thus to maintain a liquid seal across the discharge opening of the mill. As described above visual evidence that the outlet of the mill is properly sealed is obtained by allowing the liquid to also fill the space between the top plate of the trough and roller 2 as indicated by the dotted level line 39.

This arrangement provides a constant maceration liquid level in the trough above the mill discharge opening and any surplus liquid together with the bagasse flows over the over-flow edge 14 into the receptacle 17 from which it is drained at outlet 10 and recirculated to the inlets 8 and 16 by the pump 11 together with any additional liquid drawn from tank 12 to maintain the level of liquid in the trough above the output opening of the mill stage.

Details of the last mentioned arrangement including some further modifications are described hereinafter in connection with FIGURES 3 to 6.

The three rollers 1, 2 and 3 are arranged as described earlier. The chute 5 guides the prepared sugar cane into the mill from which it emerges as bagasse from the discharge opening 37 formed between the rollers 2 and 3.

This opening 37 is completely enclosed by the funnelshaped trough 13 which is filled with maceration liquid.

The trough has a rectangular cross-section, two opposite sides being formed by the two side plates 18 and 19 and the other two sides being formed by an upper plate 20 (FIGURE 5) and a lower plate 21 (FIGURE 4) arranged at diflerent angles to the horizontal plane to form a tapered funnel with the narrow lower end in contact with the rollers 2 and 3 above and below the discharge opening 37 of said rollers respectively and the upper end 38 being above the level of said opening. To achieve a good seal at the roller the lower plate carries a serrated sealing strip 44 which fits into corresponding grooves of roller 3.

The maceration liquid is passed into the funnel 13 by means of orifices 8 and 16 in the upper and lower plate respectively. The liquid is pumped from the reservoir as described above through the pipelines 22 and 23 which end in suitable heads 24 and 25 enclosing the orifices 8 and 16.

To minimise leakage of maceration liquid from the lower end of the chute the lower plate is always kept in close contact with roller 3, the plate being supported on a linkage system which is under permanent spring loading and allows a limited parallel movement of the plate (21). This is shown in FIGURE 3 for the lower plate 21 by the linkage 29 connected with a control arm 30 and under the influence of compression spring 31.

The upper ends of the plates 20 and 21 are extended by grids 32 and 33 respectively to permit surplus maceration liquid to be drained from the bagasse before the latter leaves the upper end of the trough for transportation to the next milling stage. The grid 32 extends in the same plane as the corresponding plate 20 While the lower grid 33 extends in the same plane as plate 21 with its apex at 14 serving as an overflow edge for the bagasse.

The build up of bagasse between the beginning of the top grid 32 at the end of. plate 20 and the beginning of the bottom grid 33 at the end of plate 21 and the apex 14 of grid 33 obstructs the flow of maceration liquid over apex 14 and helps to force excess maceration liquid through the upper and lower grids.

Excess maceration liquid drained through grid 33 is collected in a receptacle 17. Surplus liquid drained through grid 32 passes through a suitable opening 35 in side plate 18 into a duct 34 which connects with receptacle 17.

An outlet 10 in the lower part of receptacle 17 connects the latter by a duct 36 with a suitable pumping device for recirculation as described above in connection with FIGURE 2. i

This arrangement ensures a permanent liquid seal of the discharge opening 37 between the rollers 2 and 3 with a minimum quantity of excess maceration liquid. As described before visual evidence that the outlet of the mill is properly sealed is obtained by allowing the liquid to also fill the space between upper plate 20 and the roller 2.

The drained maceration liquid has only a small fibre content, as the bagasse itself acts as a screening agent, and is thus suitable for re-circulation with a minimum of screening.

The arrangement as described above furthermore facilitates handling of the bagasse on belt conveyors or the like, reduces the quantity of recirculated maceration liquid to a minimum and simplifies the plant thus reducing the cost of the installation.

When a milling stage is equipped with the invention no forward leakage of maceration liquid occurs through the discharge opening 37 into front roller juice either when the mill is operating normally, when the mill is running but the feed is stopped or when the mill is stopped.

Small quantities of maceration liquid in the form of a film, wetting and adhering to the surface of roller 2, are

however, carried over and will mix with front roller juice. In cases where it is important to prevent this carrying over the above film of maceration liquid may be removed from the surface of roller 2 by blowing with air jets;

The invention has been described above in connection with one milling stage only, but it must be understood that the same arrangement can be repeated for further mill stages arranged in tandem.

We claim:

1. In a milling apparatus for extracting sucrose from sugar cane in which sugar cane particles are passed through a mill with a discharge opening to discharge the resulting compressed bagasse into a maceration liquid, comprising a funnel shaped trough of substantially rectangular cross-section arranged adjacent to and across said discharge opening, said discharge opening being completely submerged in said macreation liquid to form an airtight seal for said discharge opening two opposite sides of said trough being formed by side plates of said funnel, the upper and lower sides of said funnel being formed by an upper and a lower plate each having a plurality of orifices therein, said plates being arranged at dillerent angles to the horizontal plane and extending upwards from said opening with the smaller gap between them adjacent said opening, said orifices in said upper and said lower plate being arranged nearest to said opening for the admission of maceration liquid, a grid extending from the upper plate of said funnel in the same plane thereof, a further grid extending from the lower plate in the plane of the lower plate with its outer end forming an overflow edge for said bagasse.

2. In a milling apparatus for extracting sucrose from sugarcane in which sugar cane particles are crushed becharge opening extending horizontally along said mill to discharge said bagasse into a maceration liquid, the improvements comprising side plates adjacent said opening, a first plate and a second plate extending above and below said discharge opening and abutting said plates, said first and second plates being arranged at different angles to a horizontal plane and sloping upwards to form with said side plates at downwardly tapered funnel of rectangular cross-section, said funnel having its lower end adjacent said discharge opening, a plurality of orifices in said first and said second plates adjacent said rollers, to admit maceration liquid into said funnel, a grid extending from and in the same plane with said first plate and a further grid extending from and in the same plane with said second plate, the outer end of said further grid forming an overflow edge for said bagasse, a receptacle arranged drained from said bagasse through said second grid, an

aperture in at least one of said side plates above said first plate and adjacent thereto and a duct between said aperture and said receptacle to guide maceration liquid drained through the grid in said first plate into said receptacle, pumping means for said maceration liquid and a duct from said receptacle to said pumping means, a pipeline connecting the orifices in the first plate with said pumping means, and a further pipeline connecting the orifices in said second plate With said pumping means to pump maceration liquid from said receptacle through said orifices into said funnel.

3. A milling apparatus according to claim 2 and having spring loaded linkage means pivoted at said side plates and supporting said second plate for parallel movement of said plate, said spring loaded linkage means maintaining the lower end of said plate on contact with the corresponding roller of said mill.

References Cited in the file of this patent UNITED STATES PATENTS 1,170,619 Ewart Feb. 8, 1916 1,191,826 Ramsay July 18, 1916 1,328,090 McNeil Jan. 13, 1920 1,744,286 Theile Jan. 21, 1930 1,775,830 Reynolds Sept. 16, 1930 1,846,914 Sharp Feb. 23, 1932 1,852,055 Maxwell Apr. 5, 1932 

1. IN MILLING APPARATUS FOR EXTRACTING SUCROSE FROM SUGAR CANE IN WHICH SUGAR CANE PARTICLES ARE PASSED THROUGH A MILL WITH A DISCHARGE OPENING TO DISCHARGE THE RESULTING COMPRESSED BAGASSE INTO A MACERATION LIQUID, COMPRISING A FUNNEL SHAPED TROUGH OF SUBSTANTIALLY RECTANGULAR CROSS-SECTION ARRANGED ADJACENT TO AND ACROSS SAID DISCHARGE OPENING, SAID DISCHARGE OPENING BEING COMPLETELY SUBMERGED IN SAID MACREATION LIQUID TO FORM AN AIRTIGHT SEAL FOR SAID DISCHARGE OPENING TWO OPPOSITE SIDES OF SAID TROUGH BEING FROMED BY SIDE PLATES OF SAID FUNNEL, 